We have previously utilized N-(p-azidobenzoyl)daunorubicin (NABD), a photoactive analogue of daunorubicin (DNR), to identify unique anthracycline-binding polypeptides in rodent tissues and in tumor cells. Using cultured P388 tumor cells, we have now compared the cellular pharmacology and antitumor activity of NABD with that of DNR. Although rapidly accumulated by cells, the intracellular concentration of NABD was less than 20% that of DNR at steady-state levels. The cellular uptake of both drugs by P388 cells was dependent on extracellular drug concentration in the medium and on temperature. The rapid efflux of NABD and DNR from P388 cells in drug-free medium was reduced at lowered temperature (0 degrees C). Cytofluorescence microscopy demonstrated that NABD was predominantly localized in the cytoplasm, in contrast to the nuclear localization of DNR. NABD produced dose-dependent inhibition of [3H]thymidine (IC50 = 10.0 microM) and [3H]uridine (IC50 = 1.60 microM) incorporation in P388 cells to a lesser degree than DNR ([3H]thymidine, IC50 = 0.15 microM and [3H]uridine, IC50 = 0.70 microM). Continuous exposure to NABD inhibited P388 cell proliferation with an IC50 of 0.27 microM, compared with an IC50 of 0.017 microM for DNR. NABD is a pharmacologically active, photoactive analogue of DNR, which possesses properties different from those of the parent drug but similar to those of other anthracycline analogues. Photoaffinity labeling studies with NABD may identify important cytoplasmic constituents which interact with this type of anthracycline and perhaps with the anthracycline antibiotics in general.